Portable conveyors are used for conveying bulk material, such as sand, gravel, concrete and the like. The typical portable conveyor includes an endless belt conveyor that is usually located at an inclined angle. The bulk material is fed to the lower end of the inclined conveyor and is discharged from the upper end through a hopper to a location of use.
To enable the conveyor to be readily moved between different locations on a given site, the conveyor is mounted on wheels. In the typical installation, a pair of rear wheels are located at the lower end of the conveyor, while a pair of caster wheels are supported from a horizontal axle through vertical pivot shafts and are located beneath the central portion of the conveyor.
To vary the angle of inclination of the conventional conveyor, a pair of rear arms connect the axle to the rear or lower end of the conveyor, while a pair of forward arms connect the axle to the forward or upper end of the conveyor. A cable mechanism is commonly employed to pivot the forward arms relative to the rear arms to thereby change the angle of inclination of the conveyor.
U.S. Pat. No. 4,955,955 discloses an improved mechanism for raising and lower the conveyor. In accordance with the aforementioned patent application, an adjustable linkage interconnects the axle and the conveyor. The linkage includes a pair of tie bars that interconnect the caster wheel axle and the lower portion of the conveyor, and the linkage also includes a pair of upper struts and a pair of lower struts. The lower ends of the lower struts are connected to the axle, while the upper ends of the upper struts are pivotally connected to the conveyor, and the adjacent ends of the struts are interconnected by a drive mechanism which takes the form of a threaded nut and lead screw. Operation of a hand crank operating through a set of bevel gears will rotate the lead screw mechanism to raise and lower the conveyor.
It is often desirable to be able to rapidly change the inclination of the conveyor at a construction site. However, it has been found that if the drive mechanism is designed so that it can be readily rotated through use of a manual hand crank without substantial effort, it requires a great number of time consuming revolutions of the hand crank to change the elevation. Conversely, if the drive mechanism is designed to more rapidly change the inclination, manual rotation of the hand crank can be extremely difficult.